Reply To: Antiquated typhoon warnings need changing


Email from Paul Zimmerman:

Are their 4 types of danger with typhoons? And can (should) they be anticipated/forecasted separately?

– Timing (Distance to HK) – which is the current number system. Maybe this should be replaced with actual distance?

– Wind strenght/direction – your proposal to identify the power covers this

– Rain (flooding, slips) – large and slow ones may have big rain bands – and we can use the current rain warning systems for this? Maybe stating – black rain warning is expected to be hoisted at xx time….

– Surge (Shore flooding) – isn’t this related to tide and wind strenght?

If, big if, one can differentiate the warnings, then the benefit is that people have to respond to different dangers depending on their circumstances: Ferries stop because of wind not because of rain; land slips are caused by rain not wind; etc

What u think?

My reply:

Wind – problem if above gale; danger if above storm; serious danger if above Category 3 hurricane (rare in S China Sea: see marvellous map – below – from Historical Tropical Cyclone Tracks).
Rain: not so big a trouble as massive winds could be for HK – partly as fairly used to big rainstorms in monsoons, but rainstorm warnings indeed useful.
Storm surge: maybe biggest problem of all, especially for Tolo Harbour (based on two last century). Often when I head along Tolo Harbour, rather imagine waves pushing in past science park, on towards rail line.

Current warning system starts w distance: within 800km of Hong Kong; then on to wind speeds: strong winds forecast (3), gales imminent or blowing (8), above gales happening or likely (9), and typhoon (10) – after which, nothing more, even though typhoons vary in intensity.

Tough to get mix of warnings right, as complex; very hard to predict just what trop storms will do.
Saw Sepat reach Category 5 – on hurricane scale over sea – yet rather weaker as hit Taiwan, and maybe only just typhoon strength as it hit mainland China. Even so, seen too re 900 mm rain on Taiwan:
Surging river after Sepat:
Part 2 Typhoon Sepat strikes Taiwan, biblical flooding
Sepat eyewall (not so dramatic, partly as at night):
Typhoon Sepat strikes Taiwan, eyewall + biblical floods pt 1

In US, concerns mount when get hurricanes of Category 3 and above: it seems good idea for us to have much the same system.

Also, as I’ve discussed w HK Obs before, seems good idea to have Number 8 and announce (or have special signal) that nothing much stronger than gales likely.
Hong Kong Number 8 tropical cyclone warning needs revamping?
Then, even after this discussion, I figure useful to have signal saying there looks to be real chance of winds reaching “basic” typhoon force and above.

Yes, responses can be complex. Ferries closing down important – maybe only in areas affected, if storm small: during Pabuk, ferry rides rough in western waters, while at Sai Kung winds not strong:
Pabuk the come back kid (Inc video I shot during ride into HK)
Then, more closures: buses, esp on exposed routes; and on to shutting down even all offices etc.
Very hard to get this right; inc if office has people living on Cheung Chau, others who live nearby (say). – just one example of complexity.

For storm surge: I asked Obs some time ago re this, and they do try to see if surge looking likely.
Maybe needs combination of wind strength and direction, plus high tide, and storm moving right way, to pile up water: especially Mirs Bay then into Tolo Harbour.
Hopefully there’s been some modelling etc done on this: what would surge be like along now built up shores of inner Tolo Harbour? Shore of Ma On Shan, Sha Tin along the river/channel etc.
To me, odd a “science park” appears designed without any apparent notion that one day the sea could surge along the lower levels. Where were the scientists when it was designed?
I wonder, too, re the harbour area: if waves could (just) reach Des Voeux Road during past typhoon, then some other areas today could likely be within reach of sea during violent winds (tho harder now to reach DV Rd, because of reclamation since 1962).

Been some time since strong typhoon hit Hong Kong directly, so much infrastructure is untested by real world storm.
Plus, even many locals have little idea re typhoons. Since I arrived here, just one direct hit – York, which wasn’t much above typhoon strength I think; otherwise, had quite a few Number 8s during which it seemed little happened. So, if get big storm come directly at us, might be that many people will have guard down.

Also notable – and in a way comical – I think: when major cyclones (hurricanes, typhoons, cyclones) threaten various places, from Florida to Fujian, get many people evacuated. Here, we go home and have typhoon parties! tropical_cyclone_map.gif